Gas-generating devices that utilize gas-generating grains are often used in the automotive industry for passenger restraint systems, such as for inflators for airbag modules. Additionally, new methods and devices for suppressing fires using gas-generating devices that utilize gas-generating grains have been disclosed in the aforementioned U.S. patent application Ser. No. 11/409,257 entitled MAN-RATED FIRE SUPPRESSION SYSTEM, filed on Apr. 21, 2006, now U.S. Pat. No. 8,408,222.
The following discussion relates to the environment in which embodiments of the present invention may be beneficially employed, and does not constitute Admitted Prior Art.
As gas generators are made larger, such as to produce larger amounts of gas, the inventors of the present invention discovered several issues. For example, as gas-generating grains are produced in a larger scale the reliability of the grains becomes an issue. Specifically, larger gas-generating grains tend to have an unpredictable burn rate and have an inconsistent gas production throughout the burn, as well as having other undesirable burn characteristics. Additionally, larger gas-generating grains tend to develop cracks and other structural defects that contribute to the unreliability of these larger grains and the undesirable burn characteristics of such larger grains.
Instead of a single larger grain, a plurality of smaller gas-generating grains in a single gas generator improve the reliability of the gas generator, and provide relatively predictable burn rates and relatively consistent gas production throughout the burn. However, the inventors of the present invention discovered that the interaction between the smaller, burning gas-generating grains within the gas generator has undesirable effects on the gas generator performance.
As shown in FIG. 1, a gas-generating grain 10 may have a generally annular shaped body 12 and include a plurality of protrusions 14 on a surface that may act as a “stand-off.” A plurality of grains 10 may be arranged within a sleeve 16 in a longitudinal stack, and the protrusions 14 may maintain a space between adjacent grains of the plurality of grains 10, as shown in FIG. 2A. As the grains 10 burn, the entire exposed surface of each grain 10 may combust to generate a gas. Also, as the plurality of grains 10 burns and produces gas, the size and mass of each grain 10 is reduced, as shown in FIG. 2B, and gaps 18 may be formed between adjacent grains 10.
As shown in FIG. 2C, the burning grains 10 may be accelerated in different directions during the combustion and gas-generating process and relatively large gaps 20 may result. As the burning grains 10 continue to be accelerated in various directions, the grains 10 may collide with surrounding structures and adjacent grains 10. As larger gaps 20 may form, the grains 10 may be accelerated over a greater distance, resulting in higher velocities. The collisions at such higher velocities may be relatively energetic and may result in material of the grains 10, particularly spent material of the grains 10 or so called “clinkers,” breaking apart, which may result in the production of particulates. This production of particles may be undesirable, as the gas-generating grains 10 may be enclosed within a combustion chamber of a gas-generating assembly (not shown), and as particulates are carried through the gas-generating assembly they may foul a filter of the assembly and reduce gas flow and/or may be carried out of the gas-generating assembly. The particulates that may be carried out of the gas-generating assembly may be undesirable. Additionally, excessive smoke and undesirable combustion products may result and may also be expelled from the gas-generating assembly.